There is one consideration, principally, which makes it almost certain that a function of the nerves is concerned in the results before us. This is the fact (a very important one in physiology) that the peculiar relation of the mind to the bodily organs, of which we are treating, is not alike or equal in degree to all parts; but that it seems to exist for each in some proportion to its nervous sensibility, or perhaps also to its vascularity in the healthy state:—and, still further, that the attention, strongly concentrated on one part, precludes for the moment any similar effort being exercised towards another. Admitting these circumstances as founded on observation, they lead directly to the inference that the nerves are in some manner excited by the act of attention, and that all particular and local effects on the body depend on their agency; with a secondary influence from changes in the circulation of the parts, where these effects severally occur.

Upon this conclusion, however, rises another question equally difficult, viz. with what other function of the nerves this action is most closely allied, and through what class of nerves it is carried on? Those of voluntary motion can scarcely be admitted, seeing that motion in this sense is no part of the effect, and that the influence extends to parts over which we have little or no voluntary power. The only employment of will here is in giving this partial direction to the consciousness. If, on the other hand, we suppose the nerves of sensation concerned, we must admit two several actions in opposite direction along the same tract of nerve; a condition of which, though not disproved, we have no wellassured evidence. In neither of these functions, therefore, nor in the nerves ministering to them, can we find any certain explanation of the phenomenon before us, though it has various and close relation to both, as they mutually have to each other.

In considering this intricate subject, it is impossible not to advert again to the connexion between attention, as a state of mind, and the whole class of mental emotions; a relation the more important to be noticed, because it is testified to us by many similar effects of both on the bodily organs, and may afford therefore some presumption that the same nervous agency is concerned in each case. An examination of individual consciousness will afford the best proof as to this relation. The difficulty in following it out, and that which makes it obviously needful to discriminate between the two cases, is the explicit power of the will in directing the attention of mind to particular parts. A faculty exists here distinct from mental emotion, though variously complicated with it, and especially in those instances where the attention is strongly excited by sensations derived from any organ. As a power it is equally definite as that by which we change or give direction to the trains of thought, and indeed closely allied to it in many respects.

Reverting to the question, whether there be any especial nervous action by which we thus direct the attention of mind to different organs? — and if any, what are the nerves engaged in it?—the admission must be made that we are not furnished with present means to solve the difficulty. I have tried to obtain proof in cases where there was palsy either of the nerves of sensation or of voluntary motion. But though some of the results seemed to show loss or enfeeblement of the power, particularly in the first class of cases, there was too much ambiguity from other sources to admit of certain inference. The effects upon the circulation of a part, from the consciousness thus directed to it, appear so immediate, that we might perhaps suppose the nerves belonging appropriately to the vascular system to be engaged in producing them. But, in truth, the difficulty here is one which extends

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largely over all that relates to the functions of the nervous system. Scarcely yet have all its parts been defined in reference to the two great functions of sensation and volition; while the ganglionic system, and the various nerves of organic life, are still only partially known to us in their proper actions, and yet more obscurely in their intricate connexions with the nervous powers of animal life.

The physiological fact treated of in this chapter has close relation to the faculty the mind possesses, of withdrawing itself wholly or partially from objects of sense, which yet physically impress the external organs in the same way as when fully perceived; shifting itself to other sensations, some→ times by direct effort of the will, sometimes in effect of other causes. A man may walk amidst a noisy multitude, so wrapt up in some train of separate thought, as to have neither eye nor ear for what is around him. Every moment of life, indeed, affords instances in illustration of this. We live, it may be said, in a series of acts or states; each involving the exercise of some particular faculty or sense, to the exclusion more or less of others; but all so blended, and in such subordination to the identity of the being, that we are speedily at fault in seeking to divide or analyse the succession. I doubt, however, whether sufficient notice has been taken, either by physiologists or metaphysicians, of the voluntary power the mind possesses, of separating and arranging anew objects equally and simultaneously present to the organs of sense. The phenomena both of vision and hearing offer perpetual examples of this sort of analysis of compound sensations. It is one of the bases of our intellectual existence, and well deserves all the research that can be made into its modifications.*

* In such inquiry simple examples are the best. I am looking at this

Every instance of this nature, and all the topics indeed of this chapter, are subordinate to the great inquiry regarding the relation of consciousness and volition in the sentient being, to those functions of the different organs of sense, which connect this being with its own bodily organization and with the world without. This in truth is the fundamental mystery of animal life. The difficulty, as well as importance of the questions it involves, increase, as we rise from the simpler forms of existence to those where the intellectual and moral faculties are more fully developed. In man these phenomena take their most complex character; and the ever changing relation of individual consciousness in the sentient unity, to the different bodily and mental actions which form the totality of life, illustrates best, though it may not explain, the endless varieties and seeming anomalies of human existence. Instincts, habits, insanity, dreaming, somnambulism, and trance, all come within the scope of this principle; which points out, moreover, connexions among them, not equally to be understood in any other mode of viewing the subject.

moment upon a paper of somewhat intricate pattern, covering the walls of the room. Though the pattern is one and the same, as received on the retina (the direction of the axis of vision remaining unaltered), yet, by special and separate acts of attention to its several parts, I can divide it successively into three or more distinct patterns, each producing for the time a separate impression on the mind. A certain and even difficult effort, and some time also, are required for making the translation from one apparent pattern to another; and there is difficulty in retaining any one impression before the mind, so that it does not blend with, or pass into the others both points of considerable interest, as respects the inferences to be drawn from these facts.

Experiments of this kind may be indefinitely multiplied and combined. Another, equally familiar, is that of a compound geometrical figure, as a triangle inscribed within a circle; where either the triangle or the circle may be observed alone, by directing the mind separately upon it.

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CHAP. VI.

ON POINTS WHERE A PATIENT MAY JUDGE FOR HIMSELF.

WHAT are the circumstances in which the suggestions of the patient himself may safely or expediently be admitted in the treatment of disease? Every prudent physician will make himself aware of these, in as far as they can be reduced to any thing like rule; and guide his practice more or less closely by them.

First.—The patient may almost always safely choose a temperature for himself; and inconvenience in most cases, positive harm in many, will be the effect of opposing that which he desires. His feeling here is rarely, if ever, that of theory; though too often contradicted by what is merely such. It represents in him a definite state of the body, in which the alteration of temperature desired is that best adapted for relief, and the test of its fitness usually found in the advantage resulting from the change. This rule may be taken as applicable to all fevers, even to those of the exanthematous kind; where, with an eruption on the skin, the balance between the outer and inner surfaces of the body, and the risk of repression, might seem, and actually are, of greatest importance. In whatever stage the eruption be, if the patient expressly seeks for a cooler atmosphere or cooling applications, they may be fully conceded to him, without fear of ill result; and under the guidance chiefly of his feelings as to the time during which their use may be continued. Except in some cases of vitiated sensation from nervous disease, I have scarcely ever known the judgment of a patient practically wrong on these points; and in